the very place she was standing the night of the murder. >> and i said, so the person you saw, the person you did the composite of, was that ryan ferguson? she goes, no, that was not. i go, was it chuck erickson? no, it was not. >> reporter: shefgs sure of that? >> she was absolutely sure. >> reporter: bill thought this was a huge discovery, and he started gathering other new evidence, too. but would it be enough to convince a judge his son deserved a new trial? as bill was about to find out, once a jury has found a person guilty of murder, undoing that verdict can seem, can be close to impossible. >> but no one in this case was about to give up. least of all, ryan and his family. when we come back, a new defense team and a new twist. a letter that might change everything. >> my eyes were just racing because i thought oh, my god, he's retelling the story, but now ryan's not the killer. >> when "under a killing moon" continues. experts in aroma. they're the world championship cheese judges.